Car wheel and method of making same



' Y 16, 3- I F. A. FAHRENWALD 1,908,741

GAR WHEEL AND METHOD OF MAKING SAME Filed July 6, 1929 Patented May 16,1933 UNITED STATES PATENT orries FRANK A. FAHRENWALD, O1? CHICAGO,ILLINOIS, ASSIGNOR TO SOUTHERN WHEEL COMPANY, OF NEW YORK, N. Y., ACORPORATION OF GEORGIA CAR AND METHOD OF MAKING SAME Application filedJuly 6, 1929. Serial No. 376,353.

This invention relates, to car wheels and has for its object theprovision of a new,

cheapened and improved wheel for railway rolling stock. Such wheels havelong been 5 made by casting iron into a mold of the proper shape, theperiphery of the mold consisting of a massive iron ring called achiller, which causes this exterior portion of the casting to'becomesolidified very rapidly. The composition employed for the purpose iswhatI call an unstable iron mixture, namely one which produces greycast-iron when cast in a sand mold, or white-iron when cast against achiller. A composition often used v for car wheels is carbon 3.25% to3.50%, silicon 50% to 90% and the balance iron. In such a mixture thecarbon is at least largely held in solution when the metal is melted,but the presence of silicon tends to precipitate that carbon in the formof graphite at and immediately below the temperature of solidification.The result is that when such a mixture is poured in a 'sand mold theresultant slow cooling causes the graphite to become separated out inthe form of innumerable minute graphite plates or flakes which almostcompletely interrupt the metalphase, so that the latter, although itconsists of an iron which would ordinarily be tough and ductile,exhibits the well known weakness and brittleness of cast-iron. The samematerialwhen cast in a chilled mold, pro

duces a casting, the fracture of which is.

white, like silver but very crystalline, the carbon being retained incombination with the iron in the form of a carbide known as cementite,Fe C. Such white-iron consists of a mass of cementite embraced in a continuouslphase of rather high-carbon steel. The cementite particles areextremely hard body of grey cast-iron and a tread of chilled white-iron,the chilled condition ordinarily extending into the metal a distance offrom one-half to one inch depending upon the composition of the metal.Due to the sudden cooling and the consequent contraction of theperiphery of the Wheel during the time that the hub remains not only hotbut almost molten, very severe stresses are set up, as a consequence ofwhich it is customary to remove the .chiller at the earliest possiblemoment, to lift the wheel from the mold, and to transfer it while stillred hotto a slow cooling device where it can be annealed for a period ofone or more days. According to 5 contemporary practice no fuel isemployed in this annealing operation, the wheels being merely depositedin piles of six or eightin thermally insulated pits where they- 0001 vgradually by reason of their mutually highjo temperature; and care hasbeen taken not to introduce or maintain them at an unduly hightemperature lest the treads be softened, while at the same timeintroducing them into the pits at a temperature above the criticalrange, which for this composition is about 1325 Fahrenheit. With this inview a technique has been established which will introduce the wheelsinto the pits at around 1400 to l 600 Fahrenheit.

Due to the extreme hardness of the chilled tread, wheels of this naturepossess a high reputation from the standpoint of wearing ability, butdue to the deficient tensile strength and the absolute absence ofductility A in the grey iron plate of the wheel, the expansion andcontraction of the rim due to temperature changes (caused principally bythe friction of the brakes) sometimes causes these wheels to fail bybreakage of the plates. With the-constantly increasing weights andspeeds of trains and the consequent vigorous application of the brakesthe strain upon the car wheels is constantly increasing and has nowreached a point which is upon the borderline of the ability of grey ironwheels" to stand.

Even a very small improvement in the wheel as regards toughness wouldadd a valuable factor of safety, but many years of remo search bymetallurgists all over the world have failed to produce any treatmentwhereby grey iron castings can be rendered tough or ductile. On theother hand the only alternative heretofore known has been to use steelwheels which while sufl'iciently tough and ductile, are so expensive inthe first cost and so subject to tread wear as to produce markeddisadvantages of another kind.

The objects of my invention are the provision of a new and improvedcar-wheel of castiron which shall retain the low cost of castiron, withor without a hardened tread, while possessing a degree of toughness andductility in the plate which shall better enable the latter to withstandthe necessary operating conditions; the provision of a cast-ironcarwheel having a tough strong plate; the provision of a cast-ironcar-wheel having a tough 'method of casting and heat-treating an ironcar-wheel which shall render the same tough and ductile and capable ofwithstanding present day requirements without substantial increase inits cost; the provision of a method of hardening the tread of acast-iron carwheel at the .end of its manufacturing instead of at thestart; the provision of a mode of improving the quality and strength ofcast-iron car-wheels which shall fit conveniently into the establishedtechnique and equipment of car-wheel plants; while further objects andadvantages of the invention will become apparent as the descriptionproceeds. In the drawing accompanying and forming a part of thisapplication I have illustrated certain apparatus and certain processsteps explanatory of my improvements.

Fig. 1 is a vertical sectional view through .the complete mold andpattern; Fig. 2 is a horizontal sectional view corresponding to thebroken line 22 of Fig. 1; Fig. 3 is a plan view of the drag with copeand chiller removed; Fig. 3 is a perspective view of one ..of the wedgeblocks constituting a part of i the drag; Fig. 4 is a graph showing therelation between tensile strength, temperature, and time of treatmentfor a specimen composition of chilled cast iron; Fig. 5 illustrates 9.final optional step of local tempering of the 'tread; and Fig. 6illustrates a modified mold including an auxiliary web-and-hub chiller.The pattern may be made of any desired form provided only that itobserves the stand- .ard relation of hub 1 and tread 2. The contour ofthe plate 3 which connects the two is relatively unimportant, provided,however, that for purposes of this invention it is preferably made ofsubstantially uniform thick-v .ness and is preferably formed, at leaston the bottom,with uniform surface configuration as indicated at 4,being at least devoid of abrupt shoulders. Instead of being cast in amold which is made predominantly of sand and pro- .vided only with atread-chiller, my process plate and a hard tread; the provision ofacontemplates casting practically the entire wheel under chillingconditions, with the possible exception of part of the hub and a part ofthe tread-interior regarding which it is immaterial whether they befully chilled or no. In the embodiment herein chosen for illustrativepurposes I have shown the drag made able to reduce the danger that thecasting ma be disrupted upon cooling.

have shown the middle part of the drag as consisting of a massivecircular iron block 5 formed at its center with a core-print 6 for thehub-core 7, the outside of the drag consisting of an annular metalmember 8 fashioned at 9 to form the rear face of the flange-portion ofthe tread. It is customary to dish the plate 3 considerably and to mergeeach face of the same into the tread by sweeping reverse curves 10.Unless carefully handled a rigid one-piece drag will sometimes cause arupture of the casting at some point while the same is cooling, eventhough the cope be removed as soon as the entire Wheel has solidified.For this reason I have shown an annular space 11 defined between theexterior of the part 5 and interior of the part 8, and rammed with sand12, preferably reinforced adjacent the casting by wedge-shapedchiller-blocks 13 sufficiently spaced from each other and from the block5 to permit the interposition of a layer of sand whose cushioning efiectreduces the likelihood of fracture. Suitable spacers 14; are shown 'tohold the two parts of the drag concentric.

Next above the ring 8 is the tread-chiller 15, a massive one-piece ironring, fashioned to give the desired shape to theworking surface of thetread and of its flange, and to chill the same during the casting. Thispart is identical with the device now used as standard practice in theproduction of chillediron car wheels. Suitable dowel pins 16 areemployed to attach the same to the ring 8. Resting on the chiller 15 isthe cope portion 20 of the flask, also generally made of cast iron andprovided with a large number of radially arranged cast iron plates 21adapted to help support the sand but terminating short of the surface ofthe casting. The sand 22 is rammed herein in accordance with theestablished foundry practice. A header pattern 23 is located over thehub core 7 and terminates in a plurality of sprues 24 by which thecastingis fed at several points,

while permitting ready separation of the header after pouring.

p'loy consists of:

Carbon Q' 2.85 to 3.10% Silicon 1.30 to .70% Balance iron Sulphur NotOver 20% Phosphorus Not over .60% Manganese Not over 1.

- This is a slightly lower carbon and higher silicon mixture than iscustomarily used for cast-iron car-wheels at the present time. However,it is possible to use successfully, when proper care is exercised, thestandard car-wheel iron formula which is:

Carbon 3.25 to 3.50%

Silicon .70 to .90% Balance iron Sulphur -1 Not over 20% Phosphorus Notover 50% Manganese Not over 1.

chiller 25 applied to the cope as shown in Fig. 6. Even though the plateis chilled only part way through the strength of the wheel can beimproved, since even a small improvement is important. Ordinarily thehub, which is more massive than any other portion, will turn out grey atleast in part, especially if the core be made of sand. The cope and thetread-chiller are lifted off at the earliest possible moment in order toenable the wheel to rise over the drag sufii-- ciently to permit thenecessary contraction adjacent the tread. The pouring .gate is brokenoff while white-hot, and the entire wheel carried to a heat-treatingfurnace while still at least red-hot. Promptness in this is desirablefor several reasons, among which are the saving of heat, and theincreased danger of cracking due to internal strains if allowed tobecome unduly cool.

The wheel is immediately introduced into a furnace whereby it is raisedto a temperature between 1600 (or better 1650) and 1800 Fahrenheit andwhere it is left for a period of time from twenty minutes to severalhours depending uponthe temperature and the mixture and the extent ofthe chilling and the result desired. Fig. 4 of my drawing shows therelation of toughness to time of treatment at different temperatures forthe preferred composition I have described. The result of this treatmentis to decompose the cementite portions of the casting more or lessthoroughly into graphite and pearlite. This breaking down issubstantially complete when all parts of the wheel are maintained at. atemperature of 1800 Fahrenheit for less than one hour with thecomposition stated, in case the same has been thoroughly chilled in thecasting; and how much less than one hour would produce such completedecomposition of the combined carbon depends upon the temperature of thewheel when it is introduced into the furnace and the extent of thechilling and 1 the relation of silicon to carbon in the alloy. At atemperature of 1700 Fahrenheitthe complete decomposition of thecementite is not generally accomplished even by eight hours, and at atemperature of 1650 the action is very considerably slower; I do notconsider any temperature substantially below this point as at allpractical; indeed with some mixtures not effective, within anyreasonable time. However it is not necessary to effect a completebreaking down of the cementite or liberation of combined carbon. In thefirst place the maximum toughness is attained when at least a part ofthe carbon is still retained in the combined state, and in the secondplace increase of toughness much less than the maximum attainable wouldprovide the factor of safety most sought for at this time. One conditionwhich sometimes limits the life of a grey-iron car-wheel is the thermalexpansion and contraction of its tread. While this is very small itshould be remembered that the ductility of such greyiron castings ispractically nil and no treatment ever found for such castings hasincreased it. Even a small accession of ductil ity is enough to satisfythe essential requirement of a car-wheel and after this point addedtreatment is likely to be injurious. For example, the wheels ought notto be converted into graphite and ferrite as in malleableizing for tworeasons, first because the process is long and expensive, and secondbecause a malleableized wheel would not wear well and would be too softand weak.

The extent to which this heat treatment is carried is a matter largelyof choice on the part of the manufacturer. It should be remembered thata very small improvement in the ductility of the plate only of thepresent cast-iron wheels would overcome the most serious objections;although of course the toughness of the entire wheel is even moredesirable. -With any of the above compositions cast in the mannerdescribed an exposure for from one to four hours to an atmosphere of1700 Fahrenheit is very satisfactory, though changes in compositions ortion of the metal and the nature of the heat treatment. Due tothecompaetness of the graphite inclusions ascompared with those ofordinary grey cast-iron, the resulting metal exhibits much greatertensile strength combined with a considerable degree of plastic flowunder deformation and a great ly augmented toughness. However, theseresults are obtained only in those portions of the casting which havebeen cast white by chill. It has practically no efiect on the greyportions of the casting which show primary graphite in'flake form, andthe effect on stable white-iron mixtures is extremely small. By primarygraphite I mean that graphite which is deposited in flake or plate formduring the original solidification or early cooling stages of thecasting; by secondary graphite I mean that graphite which is liberatedby the decomposition of primary cementite.

If the heat treatment should be continued sufficiently far the whiteiron portions would be converted wholly to graphite and ferrite as inmalleableizing; but this is excessive. If

arrested at an earlier stage the matrix metalconsists of a steelcomposition resembling pearlite and by suitably controlling the coolingrate an increased hardness and wearresistance can be secured. Modes ofdoing this will occur to anyone versed in working with steel. One goodway is, after removing the wheel from the furnace to surround it with anannular fluid pipe 30 provided with jet orifices 31 on its interior and,supplied with cooling fluid by a hose 32. I preferably use cold air forthis purpose, but water or oil can be used if the holes 31 aresufliciently small. In this way the tread can be hardened locally whileleaving the plate tough and strong. Owing to the considerable presenceof combined carbon in the matrix metal which results when chilled whiteiron castings are heat treated in this ma-nner it is necessary tocontrol the rate of cooling in such a way as to prevent the plate frombecoming brittle. If necessary dry sand can be piled thereon as shown at33. Any :desired succession ofvtemperatures can be employed to produce,restrain or regulate grain -'growth. It is also within my invention toallow the wheel to cool at sucha rate as to leave all the matrixportionsin a'pearlitic or other steellike condition. This means that the treadis soft and requiresoccasional dressing the same as a. soft steelwheel,but the metal produced by this machines readily and the wheels, aresoinexpensive as to render this a feasible course.

' I have also used other alloying constitu- ,ents, such as arecustomarily called hardenvanadium, manganese, or molybdenum render thecemcntite more d iflicult to break down and increase the time andtemperature required. They also tend to neutralize the effect of thesilicon and to enable more silicon to be used (and also more carbon)without producing initial grey iron. Such softeners as nickel,'copper,or aluminum may reduce the amount of silicon (or carbon) permissible orreduce the time or temperature of treatment.

It will be understood that I do not limit myself to any of the detailsherein described except as the same are recited in my several claimswhich I desire may be construed broadly each independently oflimitations contained in other claims.

Having thus described my invention what I claim is:

1. A cast-iron car-wheel having a chilled tread and also having otherportions integral therewith which contain both combined carbon and asubstantial amount of free graphite of which not more than asubstantially negligible portion occurs in flake form. g y g 2. Acar-Wheel having a chilled tread and an integral plate connecting itshub and tread, at least one face of said plate consisting of cast-ironwhich is substantially devoid of primary graphite but contains bothcombined carbon and secondary graphite, the latter in nodular form.

3. A car-wheel having a chilled tread and an integral plate connectingits hub and tread, at least one face of said plate consisting ofcast-iron containing both combined carbon and a substantial amount offree graphite of which not more than a substantially negligibleportionoccurs in primary form.

4. A car-wheel having a chilled tread and an integral plateconnectingits hub and tread, at least one face of said plate consisting of asteel-like matrix having nodular masses of secondary graphite submergedtherein. I

5. A car-wheel having a chilled tread and an integral: plate connecting.its hub and tread, said plate consisting of a metal'having the averagechemical composition of cast-iron and exhibiting a microscopic structurecharacterized by a continuous pearlitic metal phase in which aresubmerged rounded masses consisting partly of cementite and partly ofgraphite.

6. A cast-iron car-wheel having a chilled tread and an integral plateconnecting its hub and tread, said plate consisting of partiallydecomposed cementite masses embraced by a steel-like matrix.

7. A car-wheel having a chilled tread and an integral plate connectingits hub and tread said plate consisting of a metal having the averagechemical composition of cast-iron and exhibiting an internal structurecharacterized by the presence of cementite and free secondary graphiteconfined Within nodular or rounded regions.

8. A one-piece car-wheel made of a metal having at each point theaverage chemical composition of cast iron, the matrix metal of the treadportion having the physical characteristics of hardened steel and thematrix metal of the plate portion having the physical characteristics ofannealed steel, the graphite content of both portions beingsubstantially all of secondary origin.

9. A cast-iron car-Wheel characterized by the absence at least from someportion of the plate of primary graphite and the presence in said plateof secondary graphite and primary cementite. a

10. A cast-iron car-Wheel having portions which are substantially devoidof primary graphite but contain both combined carbon and secondarygraphite, the latter in nodular form.

In testimony whereof I hereunto aflix my signature. 1

FRANK A. FAHRENWALD.

